A touch panel is provided in front of a display of various devices, and is used for inputting to the device the (positional) information of a portion of the surface touched by a finger or a pen. The touch panel is used as an input device for personal computers (PCs), a variety of ticket vending machines, multi-function peripherals (MFPs), and the like. To accurately convey the input information to the device, it is desirable that the touched position on the touch panel coincides with an actual (true) display position on the display as much as possible.
However, when attaching a touch panel to a display, a positional displacement may occur therebetween. Further, in the case of a touch panel using a resistive film, non-uniformity of the resistive film may lead to a decrease in linearity of the positional information that is determined according to a resistance value, thereby causing a displacement between the touched, input position on the panel and the actual (true) display position. In general, variation of the resistance value increases at the center of the panel, and thus, the displacement between the input position touched on the panel and the true display position would increase at the center of the panel.
As a way of correcting such a displacement of the display position, there is conventionally known a method of causing an operator to touch a plurality of points on the panel or draw lines on the panel and using these correction points (lines) to estimate the displacements of the display positions over the entire panel. With this method, however, the displacement of the display position is corrected only on the points (correction points) or the lines on the panel, not in any location other than the correction points (lines).
As another conventional way of correcting the displacement of the display position, Japanese Unexamined Patent Publication (Kokai) No. 61-101829 discloses a method where a panel is divided into a plurality of areas and a correction factor is obtained for each area, and the correction factor is used to correct detected coordinates to obtain true display coordinates. In this method, however, the panel is mechanically divided into triangles of the identical shape, and according to the number of division N, a positional displacement error α is reduced to (α/N). If the displacement of the display position varies in magnitude according to the position on the panel, the displacement may not be corrected sufficiently. In other words, with this conventional method, the positional displacement may not be corrected meticulously in accordance with the positions on the panel. Since panels may have their own tendencies regarding the displacements of the display positions, it is highly likely that the conventional method cannot perform appropriate correction for each panel.